This invention relates generally to a prosthetic total knee replacement system, and more specifically to an artificial patella component of a prosthetic total knee replacement system.
The hyaline anticular cartilage of the knee joint may undergo degenerative changes due to multiple etiologies. When these degenerative changes are advanced, irreversible and unresponsive to non operative management, it may ultimately become necessary to replace the natural knee joint with an artificial knee joint prosthetic system. On many of these occasions, it is necessary to surgically implant within the natural patella an artificial patella component which then articulates with the patella femoral groove of the femoral component of the total knee joint replacement system.
When such an artificial patella component is implanted, the anticular portions of the natural patella are initially surgically removed and the subchondral bone is cut by appropriate surgical instrumentation so as to form a "patella bed" into which the artificial patella component is securely implanted. When the artificial patella component is surgically implanted in its proper location in the natural patella, the articular surface of the artificial patella component is able to articulate with the patello femoral groove of the femoral component of the knee joint prosthesis in a manner similar to the way in which the natural patella would articulate with the femur of the natural knee. As one would expect, the means for securing the artificial patella component to the natural patella should be relatively strong in order to prevent loosening of artificial patella component from the natural patella during normal usage of the knee joint prosthesis.
Different methods are known in the art for securing an artificial patella component to the natural patella. In one of these methods, the natural patella is surgically altered so as to form two cylindrical cavities proximate to the center of the natural patella. The artificial patella component, which includes a flat undersurface and a cylindrical stem portion extending anteriorly from the undersurface, is secured to the natural patella by placing the stem portion of the artificial patella component into the smaller cylindrical cavity of the natural patella. The stem portion of the artificial patella component may also include a circumferential ridge which is able to cause mechanical interference with the sides of the cylindrical cavity of the natural patella so as to attach the artificial patella component to the natural patella more securely and at times without bone cement. Bone cement is usually applied to the contact area between the artificial patella component and the natural patella in order to further secure the artificial patella component to the natural patella. Some patella designs may have more than one solid small cylindrical peg in conjunction with an undersurface groove.